Photosensitive films for graphic arts intermediates are preferred to exhibit hard gradation, high maximum density and are usually referred to as "Lith" films. Recent industry trends have demonstrated a desire for both roomlight handling and rapid development.
Silver halide based systems responding to this change have in many respects debased the performance of the inherent high sensitivity lith-developing precursor films. As such, the box to box consistency, exposure latitude, dimensional stability and image acuity have each suffered in the product evolution from darkroom-lith development to roomlight-rapid access development.
The capricious value of silver makes it difficult for both the manufacturer and user to predict future costs. Additionally, silver has been identified as a toxin to the environment and is undergoing increasing restrictions in regards to waste disposal. For each of these reasons, new films suitable for lith-film purposes have been sought. The types of films described in the literature include:
1. Roomlight handleable silver films. PA1 2. Carbon black filled or layered photo polymer films. PA1 3. Diazo-dye coupled films and PA1 4. Photo polymer-metal etch films.
Type 1 offers the advantage of product continuity and familiarity; however, the dot for dot copying capability limitations together with varying sensitivity, limited exposure latitude and of course the inherent silver cost leave substantial gaps in the performance needs.
Type 2 films such as described in European Pat. No. 0,048,160 A 1 and U.S. Pat. No. 4,229,517 are of unknown quality. However, due to the mechanical type development, they are suspected to be of limited resolution and image acuity. Additionally the use of special, dedicated processors may restrict acceptance levels.
Type 3 films lack the important black opaque characteristics as well as dot etchability and a reliable negative working analog. The requirement for special processors and the use of ammonia development further limits acceptability to the printer.
Type 4 films are generally of high quality and are etchable, but often suffer from a high degree of pinholes inherent in thin metallic layers. Their acceptability has been further burdened by the unfamiliar reflective appearance and the requirement for special processors.